Guide for the Care and Use of Laboratory Animals - Office of ...

ENVIRONMENT, hOUSING, ANd MANAGEMENT 45environmental relative humidity may be of greater importance for animalshoused in a primary enclosure in which the environmental conditions differgreatly from those of the macroenvironment (e.g., in static filter-top [isolator]cages).Some species may require conditions with high relative humidity (e.g.,selected species of nonhuman primates, tropical reptiles, and amphibians;Olson and Palotay 1983). In mice, both abnormally high and low humiditymay increase preweaning mortality (Clough 1982). In rats, low relativehumidity, especially in combination with temperature extremes, may lead toringtail, a condition involving ischemic necrosis of the tail and sometimestoes (Crippa et al. 2000; Njaa et al. 1957; Totten 1958). For some species,elevated relative humidity may affect an animal’s ability to cope with thermalextremes. Elevated microenvironmental relative humidity in rodentisolator cages may also lead to high intracage ammonia concentrations(Corning and Lipman 1991; Hasenau et al. 1993), which can be irritating tothe nasal passages and alter some biologic responses (Gordon et al. 1980;Manninen et al. 1998). In climates where it is difficult to provide a sufficientlevel of environmental relative humidity, animals should be closely monitoredfor negative effects such as excessively flaky skin, ecdysis (molting)difficulties in reptiles, and desiccation stress in semiaquatic amphibians.Ventilation and Air QualityThe primary purpose of ventilation is to provide appropriate air qualityand a stable environment. Specifically, ventilation provides an adequateoxygen supply; removes thermal loads caused by the animals, personnel,lights, and equipment; dilutes gaseous and particulate contaminants includingallergens and airborne pathogens; adjusts the moisture content andtemperature of room air; and, where appropriate, creates air pressure differentials(directional air flow) between adjoining spaces. Importantly, ventilatingthe room (i.e., the macroenvironment) does not necessarily ensureadequate ventilation of an animal’s primary enclosure (i.e., the microenvironment),that is, the air to which the animal is actually exposed. The typeof primary enclosure may considerably influence the differences betweenthese two environments—for example, differences may be negligible whenanimals are housed in open caging or pens, whereas they can be significantwhen static isolator cages are used.The volume and physical characteristics of the air supplied to a roomand its diffusion pattern influence the ventilation of an animal’s primaryenclosure and are important determinants of the animal’s microenvironment.The type and location of supply air diffusers and exhaust registersin relation to the number, arrangement, location, and type of primary andsecondary enclosures affect how well the microenvironments are ventilated